Absolute frequency measurement of a Yb optical clock at the limit of the Cs fountain
Irene Goti, Stefano Condio, Cecilia Clivati, Matias Risaro, Michele Gozzelino, Giovanni Antonio Costanzo, Filippo Levi, Davide Calonico, Marco Pizzocaro
Abstract
Abstract We present the new absolute frequency measurement of ytterbium ( 171 Yb) obtained at INRiM with the optical lattice clock IT-Yb1 against the cryogenic caesium ( 133 Cs) fountain IT-CsF2, evaluated through a measurement campaign that lasted 14 months. Measurements are performed by either using a hydrogen maser as a transfer oscillator or by synthesizing a low-noise microwave for Cs interrogation using an optical frequency comb. The frequency of the 171 Yb unperturbed clock transition <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msup> <mml:mi> </mml:mi> <mml:mn>1</mml:mn> </mml:msup> </mml:mrow> </mml:math> S <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi/> <mml:mn>0</mml:mn> </mml:msub> <mml:mo stretchy="false">→</mml:mo> <mml:mrow> <mml:msup> <mml:mi/> <mml:mn>3</mml:mn> </mml:msup> </mml:mrow> </mml:math> P 0 results to be 518 295 836 590 863.44(14) Hz, with a total fractional uncertainty of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>2.7</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>16</mml:mn> </mml:mrow> </mml:msup> </mml:math> that is limited by the uncertainty of IT-CsF2. Our measurement is in agreement with the Yb frequency recommended by the Consultative Committee for Time and Frequency. This result confirms the reliability of Yb as a secondary representation of the second and is relevant to the process of redefining the second in the International System of Units on an optical transition.